Assaults Monsters have '/assault' in their name, they can be mainly special summoned by the effect 'Assault Mode Activate!' trap card, they are useless in your hand so you may wanna keep em in your deck.

They are Synchro monster counterparts, with 500Atk/Def more, 2 levels more with a better effect, Stardust Dragon Assault is a pure example. When Assault monsters are destroyed, you usually special summon the original synchro monster back